424 



FR0CEEDING8 OF THE NATIONAL MUSEUM. 



VOli. 41. 



CALCULATION OF ELEMENTS. 



Variscite being orthorhombic, only two angular values are nec- 

 essary for a determination of the crystallograpliical elements. 

 The fundamental values of variscite are: 



&Am=(010):(110)=48° 10' 

 hAe =(010):(012) = 61° 17' . 



From these values the axial ratio is calculated and found to be: 



a:h:c = 0.8952 : 1 : 1.0957 



The measurements from which the fundamental values for variscite 

 were obtained are as follows: In the measurements of the angle (010) : 

 (110) it is possible to obtain eight values on each crystal, namely, 

 (010 : 110), (010 : TlO), (OTO : ITO), (OTO : TTO), i(110 :TlO), i(lTO : 

 TTO), 90°-KllO : ITO), 90°-*(TlO : 110). In the following table 

 only such ones of these possible eight values are given where the 

 reflections from the faces were fairly good and distinct: 



Measurements of angle b Am^^OlO) : {110). 



For the faces of e (012) the number of possible measurements was 

 not so large as the crystals measured were broken off at the lower 

 end. 



Measurements of angle h Ae={010) : {012). 



Crystal No.2 |^j ^J 



Crystal No.3 |^J ^^ 



Crystal No.4 61 28 



Crystal No.5 61 19 



Crystal No. 6. 

 Crystal No. 7. 

 Crystal No. 8. 



61 31 

 61 10 

 61 26 

 61 10 

 61 14 

 61 01 



Average of 12 measurements=61° 17', 



The only crystaUographical study hitherto made of variscite is 

 the work of Chester^ on the Arkansas mineral. He found some 



1 Chester, Albert H. Note on the crystallization of variscite. Amer. Joum. Scl., 3 ser., vol. 15, 1878, 

 p. 207. 



